1. Field of the Invention
The present invention relates to a lens barrel and an imaging apparatus.
2. Description of the Related Art
An imaging apparatus, such as a digital still camera and a digital video camera, includes a lens barrel which houses an imaging optical system for guiding a subject image to an image pickup device.
The lens barrel is configured to perform a zooming or focusing operation by moving a part of a plurality of lenses constituting the imaging optical system in optical axis directions of the lenses.
In the past, there has been a mechanism for moving a lens in the optical axis directions, which is configured to include a lens frame holding the lens and provided to be movable in the optical axis directions, and a cam barrel rotatably provided around the outer circumference of the lens frame. In the configuration, the cam barrel is rotated with a cam groove thereof engaged with a cam pin provided to the lens frame. Thereby, the lens frame is moved in the optical axis directions via the cam groove and the cam pin.
In the above-described configuration, to drive and rotate a cam ring, the outer circumference of the lens barrel is provided with a motor and a deceleration mechanism including a plurality of gear trains for transmitting the rotational driving force of the motor to the cam ring.
In this case, a minute magnetic load (e.g., detent torque) exists in the motor. The deceleration mechanism increases such a load of the motor to maintain the rotational position of the cam barrel and thereby regulate the movement of the lens frame caused by external impact. In this case, the motor may be supplied with no current or a weak current.
To provide the above-described motor and deceleration mechanism to the outer circumference of the lens barrel, however, it is necessary to secure a space in the radial direction of the lens barrel. Therefore, the configuration has a limitation in reducing the size of the lens barrel.
In view of the above, a lens barrel has been proposed which drives a lens frame by directly rotating a cam barrel by the use of a so-called hollow motor having a cylindrical open space around the axial center of a rotor (see Japanese Unexamined Patent Application Publication No. 2005-202316). In the regulation of the movement of the lens frame according to the above technique, however, it is necessary to excite the hollow motor to stop the rotation of the cam barrel. Thus, the technique is disadvantageous in power saving.
Further, another technique has been proposed which locks and unlocks a locking claw with respect to a cam barrel via a solenoid and a link mechanism in a lens barrel using a hollow motor (see Japanese Unexamined Patent Application Publication No. 6-250068).